1. Field of the Invention
The present invention relates to material testing devices and techniques, and more particularly to an arrangement for measuring the surface roughness of a workpiece.
2. Description of the Related Art
It is desirable to determine the roughness of a surface in a variety of situations. For example, a manufacturing process may involve the machining of a workpiece surface and machining introduced surface roughness may be required to be kept within certain limits. The gauging process should determine the relative roughness of a surface accurately and in a minimal amount of time.
Several devices have been developed that have as their purpose the measurement of surface roughness. The need for some measurement of surface finish for various machining operations was brought about by the necessity of having smooth bearing surfaces. The simplest procedure is a visual comparison with some established standard. Microscopic comparison is an extension of this approach. Light interference techniques to establish scratch depth has also been used. Currently known technology for determining surface roughness typically fit two categories. Contact roughness measurement measures the dimensional profile of the surface by contacting the surface with a stylus and dragging it across the surface measuring peaks and valleys. An index is then calculated based on the data collected. This process is restrictive due to the excessive amount of time required to probe the surface. Also, contact style gages utilize a fine stylus to scan the surface. Because the stylus has to be small enough to read minuscule peaks and valleys of the surface, it is susceptible to damage. Non-contact contour measurement technology utilizes a laser to scan the surface to measure the peaks and valleys. While this technology is fast, it can be significantly skewed by surface contamination. Other, more exotic techniques have been suggested including measuring surface electrical capacity, sonic transmission, or the contact angle of a drop of fluid. None of these techniques has proven to be entirely satisfactory.